Many polyurethane ionomers (PUI's) are known. The known polyurethane ionomers include polyurethane polymers that have ionic sites, which have counter ions associated with them. Some have cationic sites and are “cationomers”, and some have anionic sites, such as carboxylate and sulfonate groups, and are “anionomers”. When all of the cations associated with anionic polyurethanes (polyurethane ionomers) are protons, the materials can be described as “acid-form polyurethanes”. When some or all of the cations are metal ions, such as the Mn+ ions Na+, K+, Cs+, Li+, Mg2+, Ca2+, Sr2+, Ba2+, and Zn2+, transition metal ions, lanthamide ions or other types of cations, the materials are broadly called “ionomers”.
The known methods for preparing a polyurethane ionomer of a metal ion typically involve the reaction of a diisocyanate (or multiisocyanate) compound with two or more diol (or polyol) compounds, including at least one diol compound which contains at least one carboxylic acid group, to form an acid-form polyurethane. This step is followed by the reaction of the acid-form polyurethane with a source of metal ions, such as a metal salt. The goal is to replace the protons of the acid groups by metal ions. In principle, the products obtained using this synthetic approach can be varied by varying the isocyanate, the acid-containing diol, the other diols, the solvent, temperature, and the metal compound used for proton replacement on the acid groups of the acid-form polyurethane polymer.
Other methods for preparing polyurethane ionomers, especially polyurethane ionomers containing sulfur-containing anionic site-groups, proceed to the acid-form polyurethane in other ways. The acid-formed polyurethanes then proceed to the ionomer by reaction with a metal ion source. When both carboxylate and sulfonate acidic sites are incorporated, the carboxylate site can be introduced through reaction with a carboxylic acid diol, such as dimethylolpropionic acid (DMPA).
Some of the known polyurethane ionomers are described in the publication “Advances in Urethane Ionomers” (Edited by H. X. Xiao and K. C. Frisch, Technomic Publish Company, 1995, ISBN No. 1-56676-289-8). Others are described in the following references: S.-A. Chen and J.-S. Hsu, Polymer 34 (1993), 2769; E. Zagar and M. Zigon, Polymer, 40 (1999), 2727; C.-Z. Yang, T. G. Grasel, J. L. Bell, R. A. Register and S. L. Cooper, J. Polym. Sci., Part B: Polym. Phys., 29 (1991), 581.
Polyurethane cationomers are quite different from the anionomers. Some known polyurethane cationomers are described in the following representative references: W.-C. Chan and S.-A. Chen, Polymer, 29 (1988), 1995; S. Mohanty and N. Krishnamurti, J. Appl. Polym. Sci. 62 (1996), 1993; J. C. Lee and B. K. Kim, J. Poly. Sci., Part A: Polym. Chem., 32 (1994), 1983; X. Wei, Q. He and X. Yu, J. Appl. Polym. Sci., 67 (1998), 2179; and Shenshen Wu and Murali Rajagopalan, WO 96/40378, U.S. Pat. No. 5,692,974 and references therein.
In addition to these ionomers, there are other types of polyurethane compounds containing acidic or basic groups. Among them are polyurethane compounds which are used in latex form for coatings and finishes. Some of those polyurethane compounds designed for dispersion in polar liquids can be considered to be acid-form polyurethanes (e.g., Chien-Hsin Yang, Shih-Min Lin and Ten-Chin Wen, Polymer Science and Engineering, Vol. 35, No. 8, 722 (1995)).
The established synthetic approaches discussed above in which the acid-containing polyurethane is made and then the protons are replaced by metal ions, is referred to herein as the First Established Method (“FEM”). It involves syntheses of an acid form polyurethane directly. The cases in which a polyurethane is modified to include acid groups, such as by sulfonation, is the Second Established Method (“SEM”). These methods have led to some interesting materials with potentially valuable applications. However, the range of properties exhibited by polyurethane ionomers made using the First Established Methods is limited by the reaction process and by the compounds used in the synthesis. Moreover, the overall synthetic process is relatively slow, and it would be advantageous to have a faster synthetic procedure.
The polyurethane ionomers produced by the First Established Method (FEM) are limited by the reactants and by the synthetic process itself. This is seen in the optical and mechanical properties of the polyurethane ionomers produced by the spectral range of the First Established Method; e.g., they tend to appear cloudy. This cloudiness typically is associated with the presence of relatively large phases in non-homogeneous materials. The reasons that the FEM imposes limits on the physical properties are not fully understood, but one reason could be that in some of the syntheses there are competing reactions, such as those between the isocyanate groups and the carboxylic acid groups, that are not present or significant in the improved synthetic method (“ISM”) of the present invention. Another reason could be that the final reaction, the reaction between the acid-form polyurethane and the metal ion source, is incomplete. Even if the stoichiometrically desired proportions of acid groups and metal containing molecules are combined in that reaction, the incomplete mixing, incomplete neutralization, and process-dependent formation of ion-containing entities lead to a range of products that can be less than optimal for potential applications. In cases where the metal ion incorporation is incomplete in one of these ways, it is difficult to know what the effective metal ion content actually is, and it sometimes is impossible to know it without carrying out a chemical analysis of the final product.
A Third Established Method (“TEM”) for synthesizing polyurethane anionomers takes the advantage of the reaction of a diisocyanate (or multiisocyanate) compound with two or more diol/polyol compounds, including at least one diol or polyol compound which contains at least “one ionic group or potential ionic group”. This method is mentioned in several patents, including the following: Marek Gorzynski and Horst Schiirman, U.S. Pat. No. 4,777,224; Steve H. Ruetman and Joginder N. Anand, U.S. Pat. No. 4,956,438; and Klaus Noll and Jurgen Grammel, U.S. Pat. No. 4,092,286. The “potential ionic group” part means an acid group, as in the First Established Method described above.
Transforming the potential ionic group into its salt form often decreases the solubility of the ionic containing species and this is a problem if the synthesis of the polyurethane is carried out in an organic solvent. However, it may cause less of a problem for the synthesis of water dispersible coatings and adhesives. Clearly, the syntheses of hydrophobic thermoplastics and water dispersible coatings and the like are very different matters. As far as can be realized from a review of the prior art, when the TEM of synthesis has been employed, the reaction was carried out either in the presence of water, or was carried out with an ionic containing species that contained large hydrophobic groups to increase its solubility in non-aqueous media which has been achieved in a variety of ways, some of which are described in patents referenced above.
Consequently, the prior art methods discussed above are valuable, but they are limited by such problems as incompletely or inhomogeneously neutralized ionomers, ionomers of limited physical properties and molecular structures, and similar limitations.
Furthermore, poly (ethylene-co-acylate/methacrylate) ionomers are commercialized materials (Surlyn®, DuPont & Company and lotek™, Exxon Corporation are two commercial brands for example) and have been widely applied, as examples, on golf balls and food packaging. One disadvantage of these commercialized poly(ethylene-co-acrylate/methacrylate) ionomers is that the glass transition temperatures are above room temperature, e.g., the glass transition temperature of Surlyn® 9650 is about 50° C. Thus, the materials feel very hard in the normal human activity temperature range. This disadvantage of poly (ethylene-co-acrylate/methacrylate) ionomers makes them not the perfect candidate for producing golf balls although they are tough materials. Thus, softening the poly (ethylene-co-acrylate/methacrylate) ionomers will provide a new class of materials with more desired properties.
In order to lower the effective glass transition temperature of poly (ethylene-co-acrylate/methacrylate) ionomers, an obvious method is to blend them with a certain portion of rubbery polymer that has a glass transition temperature lower than room temperature. But in order to achieve this goal, the rubbery polymer must be miscible to a significant extent with the poly (ethylene-co-acrylate/methacrylate) ionomers, otherwise, blending of the rubber with poly (ethylene-co-acrylate/methacrylate) ionomers just leads to a material with two glass transition temperatures, one for the rubber and the other for the poly (ethylene-co-acrylate/methacrylate) ionomers. This deteriorates the mechanic strength of the original material and has no useful effect on softening the poly (ethylene-co-acrylate/methacrylate) ionomers.
Thermoplastic polyurethane ionomer rubbers with good homogeneity and ionic-site dispersal are expected to be good candidates for blending into poly (ethylene-co-acrylate/methacrylate) ionomers, because they are tough and have lower Tgs (usually around −30° to −50° C.). Thus, in this work, such high quality polyurethane ionomers were blended with poly (ethylene-co-acrylate/methacrylate) ionomers. They were found to have surprisingly high misciblities. Far-infrared spectra and dynamical mechanical thermal analysis data showed that blending occurred at the molecular level. New peaks due to ionic interactions between the polyurethane ionomers and the poly (ethylene-co-acrylate/methacrylate) ionomers were observed in the spectra of the blends. The glass transition temperature of the polyurethane ionomer in the blends was increased dramatically, which indicated that interactions between the soft segment of the polyurethane ionomers and the poly (ethylene-co-acrylate/methacrylate) ionomers occurred.